Lubricating oil compositions

ABSTRACT

Soot induced kinematic viscosity increase of lubricating oil compositions for diesel engines equipped with EGR systems can be ameliorated by selection of viscosity modifier, lubricating oil flow improvers, detergents and/or dispersants.

The present invention relates to lubricating oil compositions. Morespecifically, the present invention is directed to lubricating oilcompositions that provide improved lubricant performance in dieselengines provided with exhaust gas recirculation (EGR) systems.

BACKGROUND OF THE INVENTION

Environmental concerns have led to continued efforts to reduce theNO_(x) emissions of compression ignited (diesel) internal combustionengines. The latest technology being used to reduce the NO_(x) emissionsof diesel engines is known as exhaust gas recirculation or EGR. EGRreduces NO_(x) emissions by introducing non-combustible components(exhaust gas) into the incoming air-fuel charge introduced into theengine combustion chamber. This reduces peak flame temperature andNO_(x) generation. In addition to the simple dilution effect of the EGR,an even greater reduction in NO_(x) emission is achieved by cooling theexhaust gas before it is returned to the engine. The cooler intakecharge allows better filling of the cylinder, and thus, improved powergeneration. In addition, because the EGR components have higher specificheat values than the incoming air and fuel mixture, the EGR gas furthercools the combustion mixture leading to greater power generation andbetter fuel economy at a fixed NO_(x) generation level.

Diesel fuel contains sulfur. Even “low-sulfur” diesel fuel contains 300to 400 ppm of sulfur. When the fuel is burned in the engine, this sulfuris converted to SO_(x). In addition, one of the major by-products of thecombustion of a hydrocarbon fuel is water vapor. Therefore, the exhauststream contains some level of NO_(x), SO_(x) and water vapor. In thepast, the presence of these substances has not been problematic becausethe exhaust gases remained extremely hot, and these components wereexhausted in a disassociated, gaseous state. However, when the engine isequipped with an EGR and the exhaust gas is mixed with cooler intake airand recirculated through the engine, the water vapor can condense andreact with the NO_(x) and SO_(x) components to form a mist of nitric andsulfuric acids in the EGR stream. This phenomenon is further exacerbatedwhen the EGR stream is cooled before it is returned to the engine.

In the presence of these acids, it has been found that soot levels inlubricating oil compositions build rapidly, and that under saidconditions, the kinematic viscosity (kv) of lubricating oil compositionsincrease to unacceptable levels, even in the presence of relativelysmall levels of soot (e.g., 3 wt. % soot). Because increased lubricantviscosity adversely affects performance, and can even cause enginefailure, the use of an EGR system requires more frequent lubricantreplacement. It has been found that the simple addition of dispersantdoes not adequately address the problem.

Therefore, it would be advantageous to identify lubricating oilcompositions that better perform in diesel engines equipped with EGRsystems. Surprisingly, it has been found that by selecting certainadditives, specifically certain viscosity modifiers, dispersants and/ordetergents, and/or controlling the level and basicity of dispersantnitrogen, the rapid increase in lubricant viscosity associated with theuse of engines provided with EGR systems can be ameliorated.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided alubricating oil composition which provides improved performance indiesel engines provided with exhaust gas recirculation systems, whichlubricating oil composition has a sulfur content (of the finished oil)of less than about 0.3 wt. %, and comprises a major amount of oil oflubricating viscosity, one or more nitrogen-containing dispersants inwhich greater than 50% (by weight) of the total amount of dispersantnitrogen is non-basic, wherein the total amount of dispersantcontributes no more than about 3.5 mmols of nitrogen per 100 grams offinished oil; and one or more detergents, wherein at least 60% of thedetergent surfactant component is phenate, salicylate, or phenate andsalicylate.

In accordance with a second aspect of the invention, there is provided alubricating oil composition, as described in the first aspect, furthercomprising a minor amount of one or more high molecular weight polymerscomprising (i) copolymers of hydrogenated poly(monovinyl aromatichydrocarbon) and poly (conjugated diene), wherein the hydrogenatedpoly(monovinyl aromatic hydrocarbon) segment comprises at least about 20wt. % of the copolymer; (ii) olefin copolymers containing alkyl or arylamine, or amide groups, nitrogen-containing heterocyclic groups or esterlinkages and/or (iii) acrylate or alkylacrylate copolymer derivativeshaving dispersing groups.

In accordance with a third aspect of the invention, there is provided alubricating oil composition comprising a major amount of oil oflubricating viscosity, a minor amount of one or more high molecularweight polymers comprising (i) copolymers of hydrogenated poly(monovinylaromatic hydrocarbon) and poly (conjugated diene), wherein thehydrogenated poly(monovinyl aromatic hydrocarbon) segment comprises atleast about 20 wt. % of the copolymer; (ii) olefin copolymers containingalkyl or aryl amine, or amide groups, nitrogen-containing heterocyclicgroups or ester linkages and/or (iii) acrylate or alkylacrylatecopolymer derivatives having dispersing groups; and an amount of neutraland/or overbased phenate detergent providing said lubricating oilcomposition from about 6 to about 20 mmoles of phenate surfactant perkilogram of finished oil, wherein the lubricating oil compositioncontains less than 1 mmole of salicylate surfactant per kilogram offinished oil.

In accordance with a fourth aspect of the invention, there is provided alubricating oil composition, as described in the first, second or thirdaspect, further comprising a minor amount of a low molecular weight sootdispersing compound.

In accordance with a fifth aspect of the invention, there is provided amethod of operating a diesel engine provided with an exhaust gasrecirculation system with diesel fuel containing less than 50 ppm ofsulfur, which method comprises lubricating said engine with alubricating oil composition of the first, second, third or fourthaspect.

Other and further objects, advantages and features of the presentinvention will be understood by reference to the followingspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows diagrammatically the operation of a heavy duty dieselengine provided with an exhaust gas recirculation system that isoptionally operated in a condensing mode in which intake air and/orexhaust gas recirculation streams are cooled to below the dew point.

DETAILED DESCRIPTION OF THE INVENTION

The operation of EGR equipped diesel engines is best described withreference to FIG. 1. In such an engine, a portion of the exhaust gas isdirected from the exhaust manifold 1 of engine 8 to EGR mixer 2, inwhich the portion of the exhaust gas routed to the EGR system is mixedwith combustion air provided through air inlet 3 to form an air/exhaustgas mixture. Preferably, the portion of exhaust gas and the combustionair are cooled in an EGR cooler 4 and aftercooler 5, respectively,before being mixed. Most preferably, the portion of the exhaust gasrouted to the EGR system and/or the intake air will be cooled to adegree such that the air/exhaust gas mixture exiting EGR mixer 2 isbelow the dew point for at least 10% of the time the engine is operated.The air/exhaust gas mixture is fed to the intake manifold 6 of engine 8,mixed with fuel and combusted. Exhaust not routed to the EGR system isexhausted through exhaust outlet 7.

Preferably, the diesel engine equipped with the EGR system will befueled with a diesel fuel having low sulfur content. More preferably,the sulfur content of the fuel is less than 50 ppm, most preferably lessthan 25 ppm.

The oils of lubricating viscosity useful in the practice of theinvention may range in viscosity from light distillate mineral oils toheavy lubricating oils such as gasoline engine oils, mineral lubricatingoils and heavy duty diesel oils. Generally, the viscosity of the oilranges from about 2 mm²/sec (centistokes) to about 40 mm²/sec,especially from about 3 mm²/sec to about 20 mm²/sec, most preferablyfrom about 4 mm²/sec to about 10 mm²/sec, as measured at 100° C.

Natural oils include animal oils and vegetable oils (e.g., castor oil,lard oil); liquid petroleum oils and hydrorefined, solvent-treated oracid-treated mineral oils of the paraffinic, naphthenic and mixedparaffinic-naphthenic types. Oils of lubricating viscosity derived fromcoal or shale also serve as useful base oils.

Synthetic lubricating oils include hydrocarbon oils and halo-substitutedhydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,polybutylenes, polypropylenes, propylene-isobutylene copolymers,chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes),poly(1-decenes)); alkylbenzenes (e.g., dodecylbenzenes,tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes);polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); andalkylated diphenyl ethers and alkylated diphenyl sulfides andderivative, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof wherethe terminal hydroxyl groups have been modified by esterification,etherification, etc., constitute another class of known syntheticlubricating oils. These are exemplified by polyoxyalkylene polymersprepared by polymerization of ethylene oxide or propylene oxide, and thealkyl and aryl ethers of polyoxyalkylene polymers (e.g.,methyl-polyiso-propylene glycol ether having a molecular weight of 1000or diphenyl ether of poly-ethylene glycol having a molecular weight of1000 to 1500); and mono- and polycarboxylic esters thereof, for example,the acetic acid esters, mixed C₃-C₈ fatty acid esters and C₁₃ Oxo aciddiester of tetraethylene glycol.

Another suitable class of synthetic lubricating oils comprises theesters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkylsuccinic acids and alkenyl succinic acids, maleic acid, azelaic acid,suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic aciddimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with avariety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecylalcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycolmonoether, propylene glycol). Specific examples of such esters includesdibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctylsebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate,didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester oflinoleic acid dimer, and the complex ester formed by reacting one moleof sebacic acid with two moles of tetraethylene glycol and two moles of2-ethylhexanoic acid.

Esters useful as synthetic oils also include those made from C₅ to C₁₂monocarboxylic acids and polyols and polyol esters such as neopentylglycol, trimethylolpropane, pentaerythritol, dipentaerythritol andtripentaerythritol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- orpolyaryloxysilicone oils and silicate oils comprise another useful classof synthetic lubricants; such oils include tetraethyl silicate,tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate,tetra-(4-methyl-2-ethylhexyl)silicate,tetra-(p-tert-butyl-phenyl)silicate,hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanes andpoly(methylphenyl)siloxanes. Other synthetic lubricating oils includeliquid esters of phosphorous-containing acids (e.g., tricresylphosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid)and polymeric tetrahydrofurans.

Unrefined, refined and re-refined oils can be used in lubricants of thepresent invention. Unrefined oils are those obtained directly from anatural or synthetic source without further purification treatment. Forexample, a shale oil obtained directly from retorting operations;petroleum oil obtained directly from distillation; or ester oil obtaineddirectly from an esterification and used without further treatment wouldbe unrefined oil. Refined oils are similar to unrefined oils except thatthe oil is further treated in one or more purification steps to improveone or more properties. Many such purification techniques, such asdistillation, solvent extraction, acid or base extraction, filtrationand percolation are known to those skilled in the art. Re-refined oilsare obtained by processes similar to those used to provide refined oilsbut begin with oil that has already been used in service. Suchre-refined oils are also known as reclaimed or reprocessed oils and areoften subjected to additionally processing using techniques for removingspent additives and oil breakdown products.

The oil of lubricating viscosity may comprise a Group I, Group II, GroupIII, Group IV or Group V base stocks or base oil blends of theaforementioned base stocks. Preferably, the oil of lubricating viscosityis a Group II, Group III, Group IV or Group V base stock, or a mixturethereof, or a mixture of a Group I base stock and one or more a GroupII, Group III, Group IV or Group V base stock. The base stock, or basestock blend preferably has a saturate content of at least 65%, morepreferably at least 75%, such as at least 85%. Most preferably, the basestock, or base stock blend, has a saturate content of greater than 90%.Preferably, the oil or oil blend will have a sulfur content of less than1%, preferably less than 0.6%, most preferably less than 0.3%, byweight.

Preferably the volatility of the oil or oil blend, as measured by theNOACK test (ASTM D5880), is less than or equal to 30%, preferably lessthan or equal to 25%, more preferably less than or equal to 20%, mostpreferably less than or equal 16%. Preferably, the viscosity index (VI)of the oil or oil blend is at least 85, preferably at least 100, mostpreferably from about 105 to 140.

Definitions for the base stocks and base oils in this invention are thesame as those found in the American Petroleum Institute (API)publication “Engine Oil Licensing and Certification System”, IndustryServices Department, Fourteenth Edition, December 1996, Addendum 1,December 1998. Said publication categorizes base stocks as follows:

-   -   a) Group I base stocks contain less than 90 percent saturates        and/or greater than 0.03 percent sulfur and have a viscosity        index greater than or equal to 80 and less than 120 using the        test methods specified in Table 1.    -   b) Group II base stocks contain greater than or equal to 90        percent saturates and less than or equal to 0.03 percent sulfur        and have a viscosity index greater than or equal to 80 and less        than 120 using the test methods specified in Table 1.    -   c) Group HI base stocks contain greater than or equal to 90        percent saturates and less than or equal to 0.03 percent sulfur        and have a viscosity index greater than or equal to 120 using        the test methods specified in Table 1.    -   d) Group IV base stocks are polyalphaolefins (PAO).

e) Group V base stocks include all other base stocks not included inGroup I, II, III, or IV. TABLE 1 Analytical Methods for Base StockProperty Test Method Saturates ASTM D 2007 Viscosity Index ASTM D 2270Sulfur ASTM D 2622 ASTM D 4294 ASTM D 4927 ASTM D 3120

Metal-containing or ash-forming detergents function as both detergentsto reduce or remove deposits and as acid neutralizers or rustinhibitors, thereby reducing wear and corrosion and extending enginelife. Detergents generally comprise a polar head with a long hydrophobictail. The polar head comprises a metal salt of an acidic organiccompound. The salts may contain a substantially stoichiometric amount ofthe metal in which case they are usually described as normal or neutralsalts, and would typically have a total base number or TBN (as can bemeasured by ASTM D2896) of from 0 to 80. A large amount of a metal basemay be incorporated by reacting excess metal compound (e.g., an oxide orhydroxide) with an acidic gas (e.g., carbon dioxide). The resultingoverbased detergent comprises neutralized detergent as the outer layerof a metal base (e.g. carbonate) micelle. Such overbased detergents mayhave a TBN of 150 or greater, and typically will have a TBN of from 250to 450 or more.

Detergents that may be used include oil-soluble neutral and overbasedsulfonates, phenates, sulfurized phenates, thiophosphonates,salicylates, and naphthenates and other oil-soluble carboxylates of ametal, particularly the alkali or alkaline earth metals, e.g., barium,sodium, potassium, lithium, calcium, and magnesium. The most commonlyused metals are calcium and magnesium, which may both be present indetergents used in a lubricant, and mixtures of calcium and/or magnesiumwith sodium. Particularly convenient metal detergents are neutral andoverbased calcium sulfonates having TBN of from 20 to 450, neutral andoverbased calcium phenates and sulfurized phenates having TBN of from 50to 450 and neutral and overbased magnesium or calcium salicylates havinga TBN of from 20 to 450. Combinations of detergents, whether overbasedor neutral or both, may be used.

Sulfonates may be prepared from sulfonic acids which are typicallyobtained by the sulfonation of alkyl substituted aromatic hydrocarbonssuch as those obtained from the fractionation of petroleum or by thealkylation of aromatic hydrocarbons. Examples included those obtained byalkylating benzene, toluene, xylene, naphthalene, diphenyl or theirhalogen derivatives such as chlorobenzene, chlorotoluene andchloronaphthalene. The alkylation may be carried out in the presence ofa catalyst with alkylating agents having from about 3 to more than 70carbon atoms. The alkaryl sulfonates usually contain from about 9 toabout 80 or more carbon atoms, preferably from about 16 to about 60carbon atoms per alkyl substituted aromatic moiety.

The oil soluble sulfonates or alkaryl sulfonic acids may be neutralizedwith oxides, hydroxides, alkoxides, carbonates, carboxylate, sulfides,hydrosulfides, nitrates, borates and ethers of the metal. The amount ofmetal compound is chosen having regard to the desired TBN of the finalproduct but typically ranges from about 100 to 220 wt. % (preferably atleast 125 wt. %) of that stoichiometrically required.

Metal salts of phenols and sulfurized phenols are prepared by reactionwith an appropriate metal compound such as an oxide or hydroxide andneutral or overbased products may be obtained by methods well known inthe art. Sulfurized phenols may be prepared by reacting a phenol withsulfur or a sulfur containing compound such as hydrogen sulfide, sulfurmonohalide or sulfur dihalide, to form products which are generallymixtures of compounds in which 2 or more phenols are bridged by sulfurcontaining bridges.

Carboxylate detergents, e.g., salicylates, can be prepared by reactingaromatic carboxylic acid with an appropriate metal compound such as anoxide or hydroxide and neutral or overbased products may be obtained bymethods well known in the art. The aromatic moiety of the aromaticcarboxylic acid can contain heteroatoms, such as nitrogen and oxygen.Preferably, the moiety contains only carbon atoms; more preferably themoiety contains six or more carbon atoms; for example benzene is apreferred moiety. The aromatic carboxylic acid may contain one or morearomatic moieties, such as one or more benzene rings, either fused orconnected via alkylene bridges. The carboxylic moiety may be attacheddirectly or indirectly to the aromatic moiety. Preferably the carboxylicacid group is attached directly to a carbon atom on the aromatic moiety,such as a carbon atom on the benzene ring. More preferably, the aromaticmoiety also contains a second functional group, such as a hydroxy groupor a sulfonate group, which can be attached directly or indirectly to acarbon atom on the aromatic moiety.

Preferred examples of aromatic carboxylic acids are salicylic acids andsulfurized derivatives thereof, such as hydrocarbyl substitutedsalicylic acid and derivatives thereof. Processes for sulfurizing, forexample a hydrocarbyl—substituted salicylic acid, are known to thoseskilled in the art. Salicylic acids are typically prepared bycarboxylation, for example, by the Kolbe—Schmitt process, of phenoxides,and in that case, will generally be obtained, normally in a diluent, inadmixture with uncarboxylated phenol.

Preferred substituents in oil—soluble salicylic acids are alkylsubstituents. In alkyl—substituted salicylic acids, the alkyl groupsadvantageously contain 5 to 100, preferably 9 to 30, especially 14 to20, carbon atoms. Where there is more than one alkyl group, the averagenumber of carbon atoms in all of the alkyl groups is preferably at least9 to ensure adequate oil solubility.

Detergents generally useful in the formulation of lubricating oilcompositions also include “hybrid” detergents formed with mixedsurfactant systems, e.g., phenate/salicylates, sulfonate/phenates,sulfonate/salicylates, sulfonates/phenates/salicylates, as described,for example, in pending U.S. patent application Ser. Nos. 09/180,435 and09/180,436 and U.S. Pat. Nos. 6,153,565 and 6,281,179.

Surprisingly, it has been found that, in the presence of acids generatedduring the operation of a diesel engine provided with an exhaust gasrecirculation system, particularly an exhaust gas recirculation systemin which intake air and/or exhaust gas recirculation streams are cooledto below the dew point for at a portion of the time (e.g., at least 10%of the time) the engine is in operation, certain detergents have asignificant effect on the rate at which kinematic viscosity rises due tothe presence of soot in the lubricating oil. Specifically, it has beenfound that kinematic viscosity increases due to soot in lubricating oilcompositions in such engines can be controlled, in part, by selecting adetergent system in which from about 60% to 100% of the total amount ofdetergent surfactant is phenate and/or salicylate. Phenate neutral andoverbased detergents are preferred. Preferably, lubricating oilcompositions useful in the present invention will contain no more thanabout 30 wt. %, preferably no more than about 20 wt. %, more preferablyno more than 5 wt. % sulfonate detergent, based on the total weight ofdetergent. Preferably, the detergent system will provide the lubricatingoil composition with from about 6 to about 50 mmols, more preferablyfrom about 9 to about 40 mmols, most preferably from about 12 to about30 mmols of neutral or overbased phenate detergent surfactant, and lessthan 1 mmol of salicylate detergent surfactant per kilogram of finishedlubricant. Further preferably, the detergent system comprisessulfur-free detergent, particularly sulfur-free phenate detergent.

It is not unusual to add a detergent or other additive, to a lubricatingoil, or additive concentrate, in a diluent, such that only a portion ofthe added weight represents an active ingredient (A.I.). For example,detergent may be added together with an equal weight of diluent in whichcase the “additive” is 50% A.I. detergent. As used herein, the termweight percent (wt. %), when applied to a detergent or other additiverefers to the weight of active ingredient. Detergents conventionallycomprise from about 0.5 to about 5 wt. %, preferably from about 0.8 toabout 3.8 wt. %, most preferably from about 1.2 to about 3 wt. % of alubricating oil composition formulated for use in a heavy duty dieselengine.

Dispersants maintain in suspension materials resulting from oxidationduring use that are insoluble in oil, thus preventing sludgeflocculation and precipitation, or deposition on metal parts.Dispersants useful in the context of the present invention include therange of nitrogen-containing, ashless (metal-free) dispersants known tobe effective to reduce formation of deposits upon use in gasoline anddiesel engines, when added to lubricating oils. The ashless dispersantsof the present invention comprise an oil soluble polymeric long chainbackbone having functional groups capable of associating with particlesto be dispersed. Typically, such dispersants have amine, amine-alcoholor amide polar moieties attached to the polymer backbone, often via abridging group. The ashless dispersant may be, for example, selectedfrom oil soluble salts, esters, armino-esters, amides, imides andoxazolines of long chain hydrocarbon-substituted mono- andpolycarboxylic acids or anhydrides thereof; thiocarboxylate derivativesof long chain hydrocarbons; long chain aliphatic hydrocarbons havingpolyamine moieties attached directly thereto; and Mannich condensationproducts formed by condensing a long chain substituted phenol withformaldehyde and polyalkylene polyarirne.

Generally, each mono- or dicarboxylic acid-producing moiety will reactwith a nucleophilic group (amine or amide) and the number of functionalgroups in the polyalkenyl-substituted carboxylic acylating agent willdetermine the number of nucleophilic groups in the finished dispersant.

The polyalkenyl moiety of the dispersant of the present invention has anumber average molecular weight of from about at least about 1500,preferably between 1800 and 3000, such as between 2000 and 2800, morepreferably from about 2100 to 2500, and most preferably from about 2150to about 2400. The molecular weight of a dispersant is generallyexpressed in terms of the molecular weight of the polyalkenyl moiety asthe precise molecular weight range of the dispersant depends on numerousparameters including the type of polymer used to derive the dispersant,the number of functional groups, and the type of nucleophilic groupemployed. It is preferred that all the dispersant or dispersants used(including all nitrogen-containing dispersant and any nitrogen-freedispersant) be derived from hydrocarbon polymers having an averagenumber average molecular weight (M_(n)) of from about 1500 to about2500, preferably from about 1800 to 2400, more preferably from about2000 to about 2300.

The polyalkenyl moiety from which dispersants of the present inventionmay be derived has a narrow molecular weight distribution (MWD), alsoreferred to as polydispersity, as determined by the ratio of weightaverage molecular weight (M_(w)) to number average molecular weight(M_(n)). Specifically, polymers from which the dispersants of thepresent invention are derived have M_(w)/M_(n) of from about 1.5 toabout 2.0, preferably from about 1.5 to about 1.9, most preferably fromabout 1.6 to about 1.8.

Suitable hydrocarbons or polymers employed in the formation of thedispersants of the present invention include homopolymers, interpolymersor lower molecular weight hydrocarbons. One family of such polymerscomprise polymers of ethylene and/or at least one C₃ to C₂₈ alpha-olefinhaving the formula H₂C═CHR¹ wherein R¹ is straight or branched chainalkyl radical comprising 1 to 26 carbon atoms and wherein the polymercontains carbon-to-carbon unsaturation, preferably a high degree ofterminal ethenylidene unsaturation. Preferably, such polymers compriseinterpolymers of ethylene and at least one alpha-olefin of the aboveformula, wherein R¹ is alkyl of from 1 to 18 carbon atoms, and morepreferably is alkyl of from 1 to 8 carbon atoms, and more preferablystill of from 1 to 2 carbon atoms. Therefore, useful alpha-olefinmonomers and comonomers include, for example, propylene, butene-1,hexene-1, octene-1,4-methylpentene-1, decene-1, dodecene-1, tridecene-1,tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1,nonadecene-1, and mixtures thereof (e.g., mixtures of propylene andbutene-1, and the like). Exemplary of such polymers are propylenehomopolymers, butene-1 homopolymers, ethylene-propylene copolymers,ethylene-butene-1 copolymers, propylene-butene copolymers and the like,wherein the polymer contains at least some terminal and/or internalunsaturation. Preferred polymers are unsaturated copolymers of ethyleneand propylene and ethylene and butene-1. The interpolymers of thisinvention may contain a minor amount, e.g. 0.5 to 5 mole % of a C₄ toC₁₈ non-conjugated diolefin comonomer. However, it is preferred that thepolymers of this invention comprise only alpha-olefin homopolymers,interpolymers of alpha-olefin comonomers and interpolymers of ethyleneand alpha-olefin comonomers. The molar ethylene content of the polymersemployed in this invention is preferably in the range of 0 to 80%, andmore preferably 0 to 60%. When propylene and/or butene-1 are employed ascomonomer(s) with ethylene, the ethylene content of such copolymers ismost preferably between 15 and 50%, although higher or lower ethylenecontents may be present.

These polymers may be prepared by polymerizing alpha-olefin monomer, ormixtures of alpha-olefin monomers, or mixtures comprising ethylene andat least one C₃ to C₂₈ alpha-olefin monomer, in the presence of acatalyst system comprising at least one metallocene (e.g., acyclopentadienyl-transition metal compound) and an alumoxane compound.Using this process, a polymer in which 95% or more of the polymer chainspossess terminal ethenylidene-type unsaturation can be provided. Thepercentage of polymer chains exhibiting terminal ethenylideneunsaturation may be determined by FTIR spectroscopic analysis,titration, or C¹³ NMR. Interpolymers of this latter type may becharacterized by the formula POLY-C(R¹)═CH₂ wherein R¹ is C₁ to C₂₆alkyl, preferably C₁ to C₁₈ alkyl, more preferably C₁ to C₈ alkyl, andmost preferably C₁ to C₂ alkyl, (e.g., methyl or ethyl) and wherein POLYrepresents the polymer chain. The chain length of the R¹ alkyl groupwill vary depending on the comonomer(s) selected for use in thepolymerization. A minor amount of the polymer chains can containterminal ethenyl, i.e., vinyl, unsaturation, i.e. POLY-CH═CH₂, and aportion of the polymers can contain internal monounsaturation, e.g.POLY-CH═CH(R¹), wherein R¹ is as defined above. These terminallyunsaturated interpolymers may be prepared by known metallocene chemistryand may also be prepared as described in U.S. Pat. Nos. 5,498,809;5,663,130; 5,705,577; 5,814,715; 6,022,929 and 6,030,930.

Another useful class of polymers is polymers prepared by cationicpolymerization of isobutene, styrene, and the like. Common polymers fromthis class include polyisobutenes obtained by polymerization of a C₄refinery stream having a butene content of about 35 to about 75% by wt.,and an isobutene content of about 30 to about 60% by wt., in thepresence of a Lewis acid catalyst, such as aluminum trichloride or borontrifluoride. A preferred source of monomer for making poly-n-butenes ispetroleum feedstreams such as Raffinate II. These feedstocks aredisclosed in the art such as in U.S. Pat. No. 4,952,739. Polyisobutyleneis a most preferred backbone of the present invention because it isreadily available by cationic polymerization from butene streams (e.g.,using AlCl₃ or BF₃ catalysts). Such polyisobutylenes generally containresidual unsaturation in amounts of about one ethylenic double bond perpolymer chain, positioned along the chain. A preferred embodimentutilizes polyisobutylene prepared from a pure isobutylene stream or aRaffinate I stream to prepare reactive isobutylene polymers withterminal vinylidene olefins. Preferably, these polymers, referred to ashighly reactive polyisobutylene (HR-PIB), have a terminal vinylidenecontent of at least 65%, e.g., 70%, more preferably at least 80%, mostpreferably, at least 85%. The preparation of such polymers is described,for example, in U.S. Pat. No. 4,152,499. HR-PIB is known and HR-PIIB iscommercially available under the tradenames Glissopalm (from BASF) andUltravisT (from BP-Amoco).

Polyisobutylene polymers that may be employed are generally based on ahydrocarbon chain of from about 1800 to 3000. Methods for makingpolyisobutylene are known. Polyisobutylene can be functionalized byhalogenation (e.g. chlorination), the thermal “ene” reaction, or by freeradical grafting using a catalyst (e.g. peroxide), as described below.

The hydrocarbon or polymer backbone can be functionalized, e.g., withcarboxylic acid producing moieties (preferably acid or anhydridemoieties) selectively at sites of carbon-to-carbon unsaturation on thepolymer or hydrocarbon chains, or randomly along chains using any of thethree processes mentioned above or combinations thereof, in anysequence.

Processes for reacting polymeric hydrocarbons with unsaturatedcarboxylic acids, anhydrides or esters and the preparation ofderivatives from such compounds are disclosed in U.S. Pat. Nos.3,087,936; 3,172,892; 3,215,707; 3,231,587; 3,272,746; 3,275,554;3,381,022; 3,442,808; 3,565,804; 3,912,764; 4,110,349; 4,234,435;5,777,025; 5,891,953; as well as EP 0 382 450 B1; CA-1,335,895 andGB-A-1,440,219. The polymer or hydrocarbon may be functionalized, forexample, with carboxylic acid producing moieties (preferably acid oranhydride) by reacting the polymer or hydrocarbon under conditions thatresult in the addition of functional moieties or agents, i.e., acid,anhydride, ester moieties, etc., onto the polymer or hydrocarbon chainsprimarily at sites of carbon-to-carbon unsaturation (also referred to asethylenic or olefinic unsaturation) using the halogen assistedfunctionalization (e.g. chlorination) process or the thermal “ene”reaction.

Selective functionalization can be accomplished by halogenating, e.g.,chlorinating or brominating the unsaturated x-olefin polymer to about 1to 8 wt. %, preferably 3 to 7 wt. % chlorine, or bromine, based on theweight of polymer or hydrocarbon, by passing the chlorine or brominethrough the polymer at a temperature of 60 to 250° C., preferably 110 to160° C., e.g., 120 to 140° C., for about 0.5 to 10, preferably 1 to 7hours. The halogenated polymer or hydrocarbon (hereinafter backbone) isthen reacted with sufficient monounsaturated reactant capable of addingthe required number of functional moieties to the backbone, e.g.,monounsaturated carboxylic reactant, at 100 to 250° C., usually about180° C. to 235° C., for about 0.5 to 10, e.g., 3 to 8 hours, such thatthe product obtained will contain the desired number of moles of themonounsaturated carboxylic reactant per mole of the halogenatedbackbones. Alternatively, the backbone and the monounsaturatedcarboxylic reactant are mixed and heated while adding chlorine to thehot material.

While chlorination normally helps increase the reactivity of startingolefin polymers with monounsaturated functionalizing reactant, it is notnecessary with some of the polymers or hydrocarbons contemplated for usein the present invention, particularly those preferred polymers orhydrocarbons which possess a high terminal bond content and reactivity.Preferably, therefore, the backbone and the monounsaturatedfunctionality reactant, e.g., carboxylic reactant, are contacted atelevated temperature to cause an initial thermal “ene” reaction to takeplace. Ene reactions are known.

The hydrocarbon or polymer backbone can be functionalized by randomattachment of functional moieties along the polymer chains by a varietyof methods. For example, the polymer, in solution or in solid form, maybe grafted with the monounsaturated carboxylic reactant, as describedabove, in the presence of a free-radical initiator. When performed insolution, the grafting takes place at an elevated temperature in therange of about 100 to 260° C., preferably 120 to 240° C. Preferably,free-radical initiated grafting would be accomplished in a minerallubricating oil solution containing, e.g., 1 to 50 wt. %, preferably 5to 30 wt. % polymer based on the initial total oil solution.

The free-radical initiators that may be used are peroxides,hydroperoxides, and azo compounds, preferably those that have a boilingpoint greater than about 100° C. and decompose thermally within thegrafting temperature range to provide free-radicals. Representative ofthese free-radical initiators are azobutyronitrile,2,5-dimethylhex-3-ene-2,5-bis-tertiary-butyl peroxide and dicumeneperoxide. The initiator, when used, typically is used in an amount ofbetween 0.005% and 1% by weight based on the weight of the reactionmixture solution. Typically, the aforesaid monounsaturated carboxylicreactant material and free-radical initiator are used in a weight ratiorange of from about 1.0:1 to 30:1, preferably 3:1 to 6:1. The graftingis preferably carried out in an inert atmosphere, such as under nitrogenblanketing. The resulting grafted polymer is characterized by havingcarboxylic acid (or ester or anhydride) moieties randomly attached alongthe polymer chains: it being understood, of course, that some of thepolymer chains remain ungrafted. The free radical grafting describedabove can be used for the other polymers and hydrocarbons of the presentinvention.

The preferred monounsaturated reactants that are used to functionalizethe backbone comprise mono- and dicarboxylic acid material, i.e., acid,anhydride, or acid ester material, including (i) monounsaturated C₄ toC₁₀ dicarboxylic acid wherein (a) the carboxyl groups are vicinyl,(i.e., located on adjacent carbon atoms) and (b) at least one,preferably both, of said adjacent carbon atoms are part of said monounsaturation; (ii) derivatives of (i) such as anhydrides or C₁ to C₅alcohol derived mono- or diesters of (i); (iii) monounsaturated C₃ toC₁₀ monocarboxylic acid wherein the carbon-carbon double bond isconjugated with the carboxy group, i.e., of the structure —C═C—CO—; and(iv) derivatives of (iii) such as C₁ to C₅ alcohol derived mono- ordiesters of (iii). Mixtures of monounsaturated carboxylic materials(i)-(iv) also may be used. Upon reaction with the backbone, themonounsaturation of the monounsaturated carboxylic reactant becomessaturated. Thus, for example, maleic anhydride becomesbackbone-substituted succinic anhydride, and acrylic acid becomesbackbone-substituted propionic acid. Exemplary of such monounsaturatedcarboxylic reactants are fumaric acid, itaconic acid, maleic acid,maleic anhydride, chloromaleic acid, chloromaleic anhydride, acrylicacid, methacrylic acid, crotonic acid, cinnamic acid, and lower alkyl(e.g., C₁ to C₄ alkyl) acid esters of the foregoing, e.g., methylmaleate, ethyl fumarate, and methyl fumarate.

To provide the required functionality, the monounsaturated carboxylicreactant, preferably maleic anhydride, typically will be used in anamount ranging from about equimolar amount to about 100 wt. % excess,preferably 5 to 50 wt. % excess, based on the moles of polymer orhydrocarbon. Unreacted excess monounsaturated carboxylic reactant can beremoved from the final dispersant product by, for example, stripping,usually under vacuum, if required.

The functionalized oil-soluble polymeric hydrocarbon backbone is thenderivatized with a nitrogen-containing nucleophilic reactant, such as anamine, amino-alcohol, amide, or mixture thereof, to form a correspondingderivative. Amine compounds are preferred. Useful amine compounds forderivatizing functionalized polymers comprise at least one amine and cancomprise one or more additional amine or other reactive or polar groups.These amines may be hydrocarbyl amines or may be predominantlyhydrocarbyl amines in which the hydrocarbyl group includes other groups,e.g., hydroxy groups, alkoxy groups, amide groups, nitriles, imidazolinegroups, and the like. Particularly useful amine compounds include mono-and polyamines, e.g., polyalkene and polyoxyalkylene polyamines of about2 to 60, such as 2 to 40 (e.g., 3 to 20) total carbon atoms having about1 to 12, such as 3 to 12, preferably 3 to 9, most preferably form about6 to about 7 nitrogen atoms per molecule. Mixtures of amine compoundsmay advantageously be used, such as those prepared by reaction ofalkylene dihalide with ammonia. Preferred amines are aliphatic saturatedamines, including, for example, 1,2-diaminoethane; 1,3-diaminopropane;1,4-diaminobutane; 1,6-diaminohexane; polyethylene amines such asdiethylene triamine; triethylene tetramine; tetraethylene pentamine; andpolypropyleneamines such as 1,2-propylene diamine; anddi-(1,2-propylene)triamine. Such polyamine mixtures, known as PAM, arecommercially available. Particularly preferred polyamine mixtures aremixtures derived by distilling the light ends from PAM products. Theresulting mixtures, known as “heavy” PAM, or HPAM, are also commerciallyavailable. The properties and attributes of both PAM and/or HPAM aredescribed, for example, in U.S. Pat. Nos. 4,938,881; 4,927,551;5,230,714; 5,241,003; 5,565,128; 5,756,431; 5,792;730; and 5,854,186.

Other useful amine compounds include: alicyclic diamines such as1,4-di(aminomethyl)cyclohexane and heterocyclic nitrogen compounds suchas imidazolines. Another useful class of amines is the polyamido andrelated amido-amines as disclosed in U.S. Pat. Nos. 4,857,217;4,956,107; 4,963,275; and 5,229,022. Also usable istris(hydroxymethyl)amino methane (TAM) as described in U.S. Pat. Nos.4,102,798; 4,113,639; 4,116,876; and UK 989,409. Dendrimers, star-likeamines, and comb-structured amines may also be used. Similarly, one mayuse condensed amines, as described in U.S. Pat. No. 5,053,152. Thefunctionalized polymer is reacted with the amine compound usingconventional techniques as described, for example, in U.S. Pat. Nos.4,234,435 and 5,229,022, as well as in EP-A-208,560.

A preferred dispersant composition is one comprising at least onepolyalkenyl succinimide, which is the reaction product of a polyalkenylsubstituted succinic anhydride (e.g., PIBSA) and a polyamine (PAM) thathas a coupling ratio of from about 0.65 to about 1.25, preferably fromabout 0.8 to about 1.1, most preferably from about 0.9 to about 1. Inthe context of this disclosure, “coupling ratio” may be defined as aratio of the number of succinyl groups in the PIBSA to the number ofprimary amine groups in the polyamine reactant.

Another class of high molecular weight ashless dispersants comprisesMannich base condensation products. Generally, these products areprepared by condensing about one mole of a long chain alkyl-substitutedmono- or polyhydroxy benzene with about 1 to 2.5 moles of carbonylcompound(s) (e.g., formaldehyde and paraformaldehyde) and about 0.5 to 2moles of polyalkylene polyamine, as disclosed, for example, in U.S. Pat.No. 3,442,808. Such Mannich base condensation products may include apolymer product of a metallocene catalyzed polymerization as asubstituent on the benzene group, or may be reacted with a compoundcontaining such a polymer substituted on a succinic anhydride in amanner similar to that described in U.S. Pat. No. 3,442,808. Examples offunctionalized and/or derivatized olefin polymers synthesized usingmetallocene catalyst systems are described in the publicationsidentified supra.

The dispersant(s) of the present invention are preferably non-polymeric(e.g., are mono- or bis-succinimides).

The total amount of dispersant contributes no more than about 3.5 mmols,preferably no more than about 3 mmoles, more preferably no more thanabout 2.5 mmols of nitrogen per 100 grams of finished oil. Preferreddispersants include low-basicity dispersants, specificallynitrogen-containing dispersants in which greater than about 50 wt. %,preferably greater than about 60%, more preferably greater than about65%, most preferably greater than about 70% of the total amount ofdispersant nitrogen is non-basic of the nitrogen is non-basic. Thenormally basic nitrogen of nitrogen-containing dispersants can berendered non-basic by reacting the nitrogen-containing dispersant with asuitable, so-called “capping agent”. Conventionally, nitrogen-containingdispersants have been “capped” to reduce the adverse effect suchdispersants have on the fluoroelastomer engine seals. Numerous cappingagents and methods are known. Of the known “capping agents”, those thatconvert basic dispersant amino groups to non-basic moieties (e.g., amidoor imido groups) are most suitable. The reaction of anitrogen-containing dispersant and alkyl acetoacetate (e.g., ethylacetoacetate (EAA)) is described, for example, in U.S. Pat. Nos.4,839,071; 4,839,072 and 4,579,675. The reaction of anitrogen-containing dispersant and formic acid is described, forexample, in U.S. Pat. No. 3,185,704. The reaction product of anitrogen-containing dispersant and other suitable capping agents aredescribed in U.S. Pat. No. 4,663,064 (glycolic acid); U.S. Pat. Nos.4,612,132; 5,334,321; 5,356,552; 5,716,912; 5,849,676; 5,861,363 alkyland alkylene carbonates, e.g., ethylene carbonate); and U.S. Pat. No.4,686,054 (maleic anhydride or succinic anhydride). The foregoing listis not exhaustive and other methods of capping nitrogen-containingdispersants to convert basic amino groups to non-basic nitrogen moietiesare known to those skilled in the art.

It is preferred that that the dispersant provide the lubricating oilcomposition with from about 1 to about 7 mmols of hydroxyl (from thecapping agent) per 100 grams of finished oil. The hydroxyl moieties maycome from the use of a nitrogen-containing dispersant capped by reactionwith certain capping agents as described above, from anon-nitrogen-containing dispersant having hydroxyl functional groups, orfrom a combination thereof. Of the capping agents described above,reaction of a nitrogen-containing dispersant with alkyl acetoacetates,glycolic acid and alkylene carbonates will provide the capped dispersantwith hydroxyl moieties. In the case of alkyl acetoacetate, tautomerichydroxyl groups will be provided in equilibrium with keto groups.Non-nitrogen-containing dispersants providing hydroxyl moieties includethe reaction products of long chain hydrocarbon-substituted mono- andpolycarboxylic acids or anhydrides and mono-, bis- and/or tris-carbonylcompounds. Such materials are described, for example, in U.S. Pat. Nos.5,057,564; 5,274,051; 5,288,811 and 6,077,915; and copending U.S. patentapplication Ser. Nos. 09/476,924 and 09/781,004. Preferred aredispersant reaction products of bis-carbonyls, such as glyoxylic acid(see U.S. Pat. Nos. 5,696,060; 5,696,067; 5,777,142; 5,786,490;5,851,966 and 5,912,213); and dialkyl malonates.

It is further preferred that the dispersant or dispersants contribute,in total, from about 0.10 to about 0.18 wt. %, preferably from about0.115 to about 0.16 wt. %, most preferably from about 0.12 to about 0.14wt. % of nitrogen to the lubricating oil composition.

Low molecular weight soot dispersants useful in the formulation oflubricating oil compositions of the present invention include lowmolecular weight (compounds derived from polymer backbones having Mn ofless than about 450) nitrogen-containing compounds, and aromaticoligomeric species. Low molecular weight, nitrogen-containing compoundsthat function as soot dispersants include, for example, compounds of theformula:

wherein Ar is a mono- or polynuclear aromatic moiety;

-   -   R₁ and R₂ are independently selected from H and C₁-C₃₀        hydrocarbyl groups optionally containing one or more hetero        atoms selected from N, O and S;    -   R₃ is a C₁-C₂₀ hydrocarbyl group;    -   R₄ is H or a C₁ to C₉ hydrocarbyl group; and    -   q is 1 or2;    -   x is 1 to 3;    -   y is from 1 to 2 times the number of aromatic rings in Ar; and    -   z is zero to a number equal to the number of remaining        substitutable hydrogens on aromatic moiety Ar; and        wherein the combined number of carbon atoms in R₁, R₂, R₃ and R4        is less than 80 with the proviso that a hydroxyl group attached        to Ar can combine with N—R₁ to form a substituted or        unsubstituted 6 membered oxazine ring; with the further proviso        that, when a hydroxyl group attached to Ar combines with N—R, to        form a substituted or unsubstituted 6 membered oxazine ring, and        z is 0, R₂ is not H.

Such compounds are described in co-pending U.S. atent application Ser.No. 09/746,038. Particularly preferred compounds of Formula (I) comprisethe Mannich base reaction product of alpha- or beta-naphthol and a longchain primary or secondary amine in the presence of a carbonyl compound(e.g., formaldehyde). Such compounds may be added to lubricating oilcompositions of the present invention in amounts of from about 0.1 toabout 10 wt. %, preferably in an amount of from about 0.1 to about 2 wt.%, more preferably from about 0.1 to about 1.5 wt %, most preferablyfrom about 0.2 to about 1.2 wt. %, such as 0.3 to 1.0 wt. %, based onthe total weight of the lubricating oil composition. When used incombination with a high molecular weight nitrogen-containing dispersant,it is preferable to adjust the amount of the high molecular weightdispersant such that the nitrogen contributed to the lubricating oilcomposition from the combination of the high molecular weight dispersantand the low molecular weight nitrogen-containing compound remains withinthe range of from about 0.10 to about 0.18 wt. %, preferably from about0.115 to about 0.16 wt. %, most preferably from about 0.12 to about 0.14wt. %.

Aromatic oligomeric species useful in the formulation of lubricating oilcompositions of the present invention include compounds of the formula:

wherein each Ar independently represents an aromatic moiety selectedfrom polynuclear carbocyclic moieties, mononuclear heterocyclic moietiesand polynuclear heterocyclic moieties, said aromatic moiety beingoptionally substituted by 1 to 6 substituents selected from H, —OR₁,—N(R₁)₂, F, Cl, Br, I, -(L-(Ar)-T), —S(O)_(w)R₁, —(CZ)_(x)-(Z)_(y)-R,and -(Z)_(y)-(CZ)_(x)-R₁, wherein w is 0 to 3, each Z is independentlyO, —N(R₁)₂ or S, x and y are independently 0 or 1 and each R₁ isindependently H or a linear or branched, saturated or unsaturatedhydrocarbyl group having from 1 to about 200 carbon atoms, optionallymono- or poly-substituted with one or more groups selected from —OR₂,—N(R₂)₂, F, Cl, Br, I, —S(O)_(w)R₂, —(CZ)_(x)-(Z)_(y)-R₂ and-(Z)_(y)-(CZ)_(x)-R₂, wherein w, x, y and Z are as defined above and R₂is a hydrocarbyl group having 1 to about 200 carbon atoms;

-   -   each L is independently a linking moiety comprising a        carbon-carbon single bond or a linking group;    -   each T is independently H, OR₁, N(R₁)₂, F, Cl, Br, I,        S(O)_(w)R₁, (CZ)_(x)-(Z)_(y)-R₂ or (Z)_(y)-(CZ)_(x)-R₁, wherein        R₁, w, x, y and Z are as defined above; and    -   n is 2 to about 1000;    -   wherein at least 25% of aromatic moieties (Ar) are connected to        at least 2 linking moieties (L) and a ratio of the total number        of aliphatic carbon atoms in the oligomer to the total number of        aromatic ring atoms in aromatic moieties (Ar) is from about        0.10:1 to about 40:1.

Compounds of formula (II) are described, for example, in co-pending U.S.patent application Ser. No. 09/746,044. Preferably, Ar of formula (II)is naphthol or quinoline, with naphthol being most preferred. Thecompound of formula (II) may be added to lubricating oil compositions ofthe present invention in amounts of from about 0.0005 to about 10 wt. %,preferably in an amount of from about 0.1 to about 2 wt. %, morepreferably from about 0.1 to about 1.5 wt %, most preferably from about0.2 to about 1.2 wt. %, such as 0.3 to 1.0 wt. %, based on the totalweight of the lubricating oil composition.

The viscosity index of the base stock is increased, or improved, byincorporating therein certain polymeric materials that function asviscosity modifiers (VM) or viscosity index improvers (VII). Generally,polymeric materials useful as viscosity modifiers are those havingnumber average molecular weights (Mn) of from about 5,000 to about250,000, preferably from about 15,000 to about 200,000, more preferablyfrom about 20,000 to about 150,000. These viscosity modifiers can begrafted with grafting materials such as, for example, maleic anhydride,and the grafted material can be reacted with, for example, amines,amides, nitrogen-containing heterocyclic compounds or alcohol, to formmultifunctional viscosity modifiers (dispersant-viscosity modifiers).

Pour point depressants (PPD), otherwise known as lube oil flow improvers(LOFIs) lower the temperature. Compared to VM, LOFIs generally have alower number average molecular weight. Like VM, LOFIs can be graftedwith grafting materials such as, for example, maleic anhydride, and thegrafted material can be reacted with, for example, amines, amides,nitrogen-containing heterocyclic compounds or alcohol, to formmultifunctional additives.

Polymer molecular weight, specifically Mn, can be determined by variousknown techniques. One convenient method is gel permeation chromatography(GPC), which additionally provides molecular weight distributioninformation (see W. W. Yau, J. J. Kirkland and D. D. Bly, “Modern SizeExclusion Liquid Chromatography”, John Wiley and Sons, New York, 1979).Another useful method for determining molecular weight, particularly forlower molecular weight polymers, is vapor pressure osmometry (see, e.g.,ASTM D3592).

One class of polymers that can be used as the “high molecular polymer”of the present invention is copolymers of hydrogenated poly(monovinylaromatic hydrocarbon) and poly (conjugated diene), wherein thehydrogenated poly(monovinyl aromatic hydrocarbon) segment comprises atleast about 20 wt. % of the copolymer (hereinafter “Polymer (i)”). Suchpolymers can be used in lubricating oil compositions as viscositymodifiers and are commercially available as, for example, SV151(Infineum USA L.P.). Preferred monovinyl aromatic hydrocarbon monomersuseful in the formation of such materials include styrene,alkyl-substituted styrene, alkoxy-substituted styrene, vinyl naphthaleneand alkyl-substituted vinyl naphthalene. The alkyl and alkoxysubstituents may typically comprise from 1 to 6 carbon atoms, preferablyfrom 1 to 4 carbon atoms. The number of alkyl or alkoxy substituents permolecule, if present, may range from 1 to 3, and is preferably one.

Preferred conjugated diene monomers useful in the formation of suchmaterials include those conjugated dienes containing from 4 to 24 carbonatoms, such as 1,3-butadiene, isoprene, piperylene, methylpentadiene,2-phenyl-1,3-butadiene, 3,4-dimethyl-1,3-hexadiene and4,5-diethyl-1,3-octadiene.

Preferred are block copolymers comprising at least one poly(monovinylaromatic hydrocarbon) block and at least one poly (conjugated diene)block. Preferred block copolymers are selected from those of the formulaAB, wherein A represents a block polymer of predominantly poly(monovinylaromatic hydrocarbon), B represents a block of predominantly poly(conjugated diene).

Preferably, the poly(conjugated diene) block is partially or fullyhydrogenated. More preferably, the monovinyl aromatic hydrocarbons arestyrene and/or alkyl-substituted styrene, particularly styrene.Preferred conjugated dienes are those containing from 4 to 12 carbonatoms, more preferably from 4 to 6 carbon atoms. Isoprene and butadieneare the most preferred conjugated diene monomers. Preferably, thepoly(isoprene) is hydrogenated.

Block copolymers and selectively hydrogenated block copolymers are knownin the art and are commercially available. Such block copolymers can bemade can be made by anionic polymerization with an alkali metalinitiator such as sec-butyllithium, as described, for example, in U.S.Pat. Nos. 4,764,572; 3,231,635; 3,700,633 and 5,194,530.

The poly(conjugated diene) block(s) of the block copolymer may beselectively hydrogenated, typically to a degree such that the residualethylenic unsaturation of the block is reduced to at most 20%, morepreferably at most 5%, most preferably at most 2% of the unsaturationlevel before hydrogenation. The hydrogenation of these copolymers may becarried out using a variety of well established processes includinghydrogenation in the presence of such catalysts as Raney Nickel, noblemetals such as platinum and the like, soluble transition metal catalystsand titanium catalysts as described in U.S. Pat. No. 5,299,464.

Sequential polymerization or reaction with divalent coupling agents canbe used to form linear polymers. It is also known that a coupling agentcan be formed in-situ by the polymerization of a monomer having twoseparately polymerizable vinyl groups such a divinylbenzene to providestar polymers having from about 6 to about 50 arms. Di- and multivalentcoupling agents containing 2 to 8 functional groups, and methods offorming star polymers are well known and such materials are availablecommercially.

A second class of polymers useful in the practice of the presentinvention are olefin copolymers (OCP) containing dispersing groups suchas alkyl or aryl amine, or amide groups, nitrogen-containingheterocyclic groups or ester linkages (hereinafter “Polymer (ii)”). Theolefin copolymers can comprise any combination of olefin monomers, butare most commonly ethylene and at least one other α-olefin. The at leastone other α-olefin monomer is conventionally an α-olefin having 3 to 18carbon atoms, and is most preferably propylene. As is well known,copolymers of ethylene and higher α-olefins, such as propylene, ofteninclude other polymerizable monomers. Typical of these other monomersare non-conjugated dienes such as the following, non-limiting examples

-   -   a. straight chain dienes such as 1,4-hexadiene and        1,6-octadiene;    -   b. branched chain acyclic dienes such as 5-methyl-1,4-hexadiene;        3,7-dimethyl-1,6-octadiene; 3,7-dimethyl-1,7-octadiene and mixed        isomers of dihydro-mycene and dihydroocinene;    -   c. single ring alicyclic dienes such as 1,4-cyclohexadiene;        1,5-cyclooctadiene; and 1,5-cyclododecadiene;    -   d. multi-ring alicyclic fused and bridged ring dienes such as        tetrahydroindene; methyltetrahydroindene; dicyclopentadiene;        bicyclo-(2,2,1 )-hepta-2,5-diene; alkenyl, alkylidene,        cycloalkenyl and cycloalkylidene norbornenes such as        5-methylene-2-norbornene (MNB), 5-ethylidene-2-norbornene (ENB),        5-propylene-2-norbornene, 5-isoproylidene-2-norbornene,        5-(4-cyclopentyenyl)-2-norbornene;        5-cyclohexylidene-2-norbornene.

Of the non-conjugated dienes typically used, dienes containing at leastone of the double bonds in a strained ring are preferred. The mostpreferred diene is 5-ethylidene-2-norbornene (ENB). The amount of diene(wt. basis) in the copolymer can be from 0% to about 20%, with 0% toabout 15% being preferred, and 0% to about 10% being most preferred. Asalready noted, the most preferred olefin copolymer isethylene-propylene. The average ethylene content of the copolymer can beas low as 20% on a weight basis. The preferred minimum ethylene contentis about 25%. A more preferred minimum is 30%. The maximum ethylenecontent can be as high as 90% on a weight bas, preferably the maximumethylene content is 85%, most preferably about 80%. Preferably, theolefin copolymers contain from about 35 to 75 wt. % ethylene, morepreferably from about 50 to about 70 wt. % ethylene.

The molecular weight (number average) of the olefin copolymer can be aslow as 2000, but the preferred minimum is 10,000. The more preferredminimum is 15,000, with the most preferred minimum number averagemolecular weight being 20,000. It is believed that the maximum numberaverage molecular weight can be as high as 12,000,000. The preferredmaximum is about 1,000,000, with the most preferred maximum being about750,000. An especially preferred range of number average molecularweight for the olefin copolymers of the present invention is from about50,000 to about 500,000.

Olefin copolymers can be rendered multifunctional by attaching anitrogen-containing polar moiety (e.g., amine, amine-alcohol or amide)to the polymer backbone. The nitrogen-containing moieties areconventionally of the formula R—N—R′R″, wherein R, R′ and R″ areindependently alkyl, aryl of H. Also suitable are aromatic amines of theformula R—R′—NH—R″—R, wherein R′ and R″ are aromatic groups and each areis alkyl. The most common method for forming a multifunctional OCPviscosity modifier involves the free radical addition of thenitrogen-containing polar moiety to the polymer backbone. Thenitrogen-containing polar moiety can be attached to the polymer using adouble bond within the polymer (i.e., the double bond of the dieneportion of an EPDM polymer, or by reacting the polymer with a compoundproviding a bridging group containing a double bond (e.g., maleicanhydride as described, for example, in U.S. Pat. Nos. 3,316,177;3,326,804; and carboxylic acids and ketones as described, for example,in U.S. Pat. No. 4,068,056), and subsequently derivatizing thefunctionalized polymer with the nitrogen-containing polar moiety. A morecomplete list of nitrogen-containing compounds that can be reacted withthe functionalized OCP are described infra, in the discussion ofdispersants. Multifunctionalized OCPs and methods for forming suchmaterials are known in the art and are available commercially (e.g.,HITEC 5777 available from Ethyl Corporation and PA1160, a product ofDutch Staaten Minen).

Preferred are low ethylene olefin copolymers containing about 50 wt. %ethylene and having a number average molecular weight between 10,000 and20,000 grafted with maleic anhydride and aminated withaminophenyldiamine and other dispersant amines.

The third class of polymers useful in the practice of the presentinvention are acrylate or alkylacrylate copolymer derivatives havingdispersing groups (hereinafter “Polymer (iii)”). These polymers havebeen used as multifunctional dispersant viscosity modifiers inlubricating oil compositions, and lower molecular weight polymers ofthis type have been used as multifunctional dispersant/LOFIs. Suchpolymers are commercially available as, for example, ACRYLOID 954, (aproduct of RohMax USA Inc.) The acrylate or methacrylate monomers andalkyl acrylate or methacrylate monomers useful in the formation ofPolymer (iii) can be prepared from the corresponding acrylic ormethacrylic acids or their derivatives. Such acids can be derived usingwell known and conventional techniques. For example, acrylic acid can beprepared by acidic hydrolysis and dehydration of ethylene cyanohydrin orby the polymerization of β-propiolactone and the destructivedistillation of the polymer to form acrylic acid. Methacrylic acid canbe prepared by, for example, oxidizing a methyl α-alkyl vinyl ketonewith metal hypochlorites; dehydrating hydroxyisobutyric acid withphosphorus pentoxide; or hydrolyzing acetone cyanohydrin.

Alkyl acrylates or methacrylate monomers can be prepared by reacting thedesired primary alcohol with the acrylic acid or methacrylic acid in aconventional esterification catalyzed by acid, preferably p-toluenesulfonic acid and inhibited from polymerization by MEHQ or hydroquinone.Suitable alkyl acrylates or alkyl methacrylates contain from about 1 toabout 30 carbon atoms in the alkyl carbon chain. Typical examples ofstarting alcohols include methyl alcohol, ethyl alcohol, ethyl alcohol,butyl alcohol, octyl alcohol, iso-octyl alcohol, isodecyl alcohol,undecyl alcohol, dodecyl alcohol, tridecyl alcohol, capryl alcohol,lauryl alcohol, myristyl alcohol, pentadecyl alcohol, palmityl alcoholand stearyl alcohol. The starting alcohol can be reacted with acrylicacid or methacrylic acid to form the desired acrylates andmethacrylates, respectively. These acrylate polymers may have numberaverage molecular weights (Mn) of 10,000-1,000,000 and preferably themolecular weight range is from about 200,000-600,000.

To provide an acrylate or methacrylate with a dispersing group, theacrylate or methacrylate monomer is copolymerized with anamine-containing monomer or the acrylate or methacrylate main chainpolymer is provided so as to contain sights suitable for grafting andthen amine-containing branches are grafted onto the main chain bypolymerizing amine-containing monomers.

Examples of amine-containing monomers include the basic aminosubstituted olefins such as p-(2-diethylaminoethyl) styrene; basicnitrogen-containing heterocycles having a polymerizable ethylenicallyunsaturated substituent such as the vinyl pyridines or the vinylpyrrolidones; esters of amino alcohols with unsaturated carboxylic acidssuch as dimethylaminoethyl methacrylate and polymerizable unsaturatedbasic amines such as allyl amine.

Preferred Polymer (iii) materials include polymethacrylate copolymersmade from a blend of alcohols with the average carbon number of theester between 8 and 12 containing between 0.1-0.4% nitrogen by weight.

Most preferred are polymethacrylate copolymers made from a blend ofalcohols with the average carbon number of the ester between 9 and 10containing between 0.2-0.25% nitrogen by weight provided in the form ofN-N Dimethylaminoalkyl-methacrylate.

Lubricating oil compositions useful in the practice of the presentinvention contain Polymer (i), (ii), (iii), or a mixture thereof, in anamount of from about 0.10 to about 2 wt. %, based on polymer weight;more preferably from about 0.2 to about 1 wt. %, most preferably fromabout 0.3 to about 0.8 wt. %. Alternatively in discussing themultifunctional components; specifically Polymers (ii) and (iii); saidcomponents are present providing nitrogen content to the lubricating oilcomposition from about 0.0001 to about 0.02 wt. %, preferably from about0.0002 to about 0.01 wt. %, most preferably from about 0.0003 to about0.008 wt. % of nitrogen. Polymers (i), (ii) (iii) and mixtures thereof,need not comprise the sole VM and/or LOFI in the lubricating oilcomposition, and other VM, such as non-functionalized olefin copolymerVM and, for example, alkylfumarate/vinyl acetate copolymer LOFIs may beused in combination therewith. For example, a heavy duty diesel engineof the present invention may be lubricated with a lubricating oilcomposition wherein the high molecular weight polymer is a mixturecomprising from about 10 to about 90 wt. % of a hydrogenatedstyrene-isoprene block copolymer, and from about 10 to about 90 wt. %non-functionalized OCP.

Additional additives may be incorporated into the compositions of theinvention to enable particular performance requirements to be met.Examples of additives which may be included in the lubricating oilcompositions of the present invention are metal rust inhibitors,viscosity index improvers (other than polymer i, iii and/or iii),corrosion inhibitors, oxidation inhibitors, friction modifiers,anti-foaming agents, anti-wear agents and pour point depressants (otherthan polymer iii). Some are discussed in further detail below.

Dihydrocarbyl dithiophosphate metal salts are frequently used asantiwear and antioxidant agents. The metal may be an alkali or alkalineearth metal, or aluminum, lead, tin, molybdenum, manganese, nickel orcopper. The zinc salts are most commonly used in lubricating oil inamounts of 0.1 to 10, preferably 0.2 to 2 wt. %, based upon the totalweight of the lubricating oil composition. They may be prepared inaccordance with known techniques by first forming a dihydrocarbyldithiophosphoric acid (DDPA), usually by reaction of one or more alcoholor a phenol with P₂S₅ and then neutralizing the formed DDPA with a zinccompound. For example, a dithiophosphoric acid may be made by reactingmixtures of primary and secondary alcohols. Alternatively, multipledithiophosphoric acids can be prepared where the hydrocarbyl groups onone are entirely secondary in character and the hydrocarbyl groups onthe others are entirely primary in character. To make the zinc salt, anybasic or neutral zinc compound could be used but the oxides, hydroxidesand carbonates are most generally employed. Commercial additivesfrequently contain an excess of zinc due to the use of an excess of thebasic zinc compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil soluble saltsof dihydrocarbyl dithiophosphoric acids and may be represented by thefollowing formula:

wherein R and R′ may be the same or different hydrocarbyl radicalscontaining from 1 to 18, preferably 2 to 12, carbon atoms and includingradicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl andcycloaliphatic radicals. Particularly preferred as R and R′ groups arealkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, forexample, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl,amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl,2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl,propenyl, butenyl. In order to obtain oil solubility, the total numberof carbon atoms (i.e. R and R′) in the dithiophosphoric acid willgenerally be about 5 or greater. The zinc dihydrocarbyl dithiophosphatecan therefore comprise zinc dialkyl dithiophosphates. The presentinvention may be particularly useful when used with lubricantcompositions containing phosphorus levels of from about 0.02 to about0.12 wt. %, preferably from about 0.03 to about 0.10 wt. %. Morepreferably, the phosphorous level of the lubricating oil compositionwill be less than about 0.08 wt. %, such as from about 0.05 to about0.08 wt. %.

Oxidation inhibitors or antioxidants reduce the tendency of mineral oilsto deteriorate in service. Oxidative deterioration can be evidenced bysludge in the lubricant, varnish-like deposits on the metal surfaces,and by viscosity growth. Such oxidation inhibitors include hinderedphenols, alkaline earth metal salts of alkylphenolthioesters havingpreferably C₅ to C₁₂ alkyl side chains, calcium nonylphenol sulfide, oilsoluble phenates and sulfurized phenates, phosphosulfurized orsulfurized hydrocarbons or esters, phosphorous esters, metalthiocarbamates, oil soluble copper compounds as described in U.S. Pat.No. 4,867,890, and molybdenum-containing compounds.

Aromatic amines having at least two aromatic groups attached directly tothe nitrogen constitute another class of compounds that is frequentlyused for antioxidancy. While these materials may be used in smallamounts, preferred embodiments of the present invention are free ofthese compounds. They are preferably used in only small amounts, i.e.,up to 0.4 wt. %, or more preferably avoided altogether other than suchamount as may result as an impurity from another component of thecomposition.

Typical oil soluble aromatic amines having at least two aromatic groupsattached directly to one amine nitrogen contain from 6 to 16 carbonatoms. The amines may contain more than two aromatic groups. Compoundshaving a total of at least three aromatic groups in which two aromaticgroups are linked by a covalent bond or by an atom or group (e.g., anoxygen or sulfur atom, or a —CO—, —SO₂— or alkylene group) and two aredirectly attached to one amine nitrogen also considered aromatic amineshaving at least two aromatic groups attached directly to the nitrogen.The aromatic rings are typically substituted by one or more substituentsselected from alkyl, cycloalkyl, alkoxy, aryloxy, acyl, acylamino,hydroxy, and nitro groups. The amount of any such oil soluble aromaticamines having at least two aromatic groups attached directly to oneamine nitrogen should preferably not exceed 0.4 wt. % active ingredient.

Preferably, lubricating oil compositions in accordance with the presentinvention contain from about 0.05 to about 5 wt. %, preferably fromabout 0.10 to about 3 wt. %, most preferably from about 0.20 to about1.5 wt. % of phenolic antioxidant, based on the total weight of thelubricating oil composition. Even more preferably, lubricating oilcompositions in accordance with the present invention contain phenolicantioxidant in the amount set forth above, and comprise less than 0.1wt. %, based on the total weight of the lubricating oil composition,aromatic amine antioxidant.

Friction modifiers and fuel economy agents that are compatible with theother ingredients of the final oil may also be included. Examples ofsuch materials include glyceryl monoesters of higher fatty acids, forexample, glyceryl mono-oleate; esters of long chain polycarboxylic acidswith diols, for example, the butane diol ester of a dimerizedunsaturated fatty acid; oxazoline compounds; and alkoxylatedalkyl-substituted mono-amines, diamines and alkyl ether amines, forexample, ethoxylated tallow amine and ethoxylated tallow ether amine. Apreferred lubricating oil composition contains a dispersant compositionof the present invention, base oil, and a nitrogen-containing frictionmodifier.

Other known friction modifiers comprise oil-soluble organo-molybdenumcompounds. Such organo-molybdenum friction modifiers also provideantioxidant and antiwear credits to a lubricating oil composition. As anexample of such oil soluble organo-molybdenum compounds, there may bementioned the dithiocarbamates, dithiophosphates, dithiophosphinates,xanthates, thioxanthates, sulfides, and the like, and mixtures thereof.Particularly preferred are molybdenum dithiocarbamates,dialkyldithiophosphates, alkyl xanthates and alkylthioxanthates.

Additionally, the molybdenum compound may be an acidic molybdenumcompound. These compounds will react with a basic nitrogen compound asmeasured by ASTM test D-664 or D-2896 titration procedure and aretypically hexavalent. Included are molybdic acid, ammonium molybdate,sodium molybdate, potassium molybdate, and other alkaline metalmolybdates and other molybdenum salts, e.g., hydrogen sodium molybdate,MoOCl₄, MoO₂Br₂, Mo₂O₃Cl₆, molybdenum trioxide or similar acidicmolybdenum compounds.

Among the molybdenum compounds useful in the compositions of thisinvention are organo-molybdenum compounds of the formulaMo(ROCS₂)₄ andMo(RSCS₂)₄wherein R is an organo group selected from the group consisting ofalkyl, aryl, aralkyl and alkoxyalkyl, generally of from 1 to 30 carbonatoms, and preferably 2 to 12 carbon atoms and most preferably alkyl of2 to 12 carbon atoms. Especially preferred are thedialkyldithiocarbamates of molybdenum.

Another group of organo-molybdenum compounds useful in the lubricatingcompositions of this invention are trinuclear molybdenum compounds,especially those of the formula Mo3S_(k)L_(n)Q_(z) and mixtures thereofwherein the L are independently selected ligands having organo groupswith a sufficient number of carbon atoms to render the compound solubleor dispersible in the oil, n is from 1 to 4, k varies from 4 through 7,Q is selected from the group of neutral electron donating compounds suchas water, amines, alcohols, phosphines, and ethers, and z ranges from 0to 5 and includes non-stoichiometric values. At least 21 total carbonatoms should be present among all the ligands' organo groups, such as atleast 25, at least 30, or at least 35 carbon atoms.

The ligands are independently selected from the group of

and mixtures thereof, wherein X, X₁, X₂, and Y are independentlyselected from the group of oxygen and sulfur, and wherein R₁, R₂, and Rare independently selected from hydrogen and organo groups that may bethe same or different. Preferably, the organo groups are hydrocarbylgroups such as alkyl (e.g., in which the carbon atom attached to theremainder of the ligand is primary or secondary), aryl, substituted aryland ether groups. More preferably, each ligand has the same hydrocarbylgroup.

The term “hydrocarbyl” denotes a substituent having carbon atomsdirectly attached to the remainder of the ligand and is predominantlyhydrocarbyl in character within the context of this invention. Suchsubstituents include the following:

1. Hydrocarbon substituents, that is, aliphatic (for example alkyl oralkenyl), alicyclic (for example cycloalkyl or cycloalkenyl)substituents, aromatic-, aliphatic- and alicyclic-substituted aromaticnuclei and the like, as well as cyclic substituents wherein the ring iscompleted through another portion of the ligand (that is, any twoindicated substituents may together form an alicyclic group).

2. Substituted hydrocarbon substituents, that is, those containingnon-hydrocarbon groups which, in the context of this invention, do notalter the predominantly hydrocarbyl character of the substituent. Thoseskilled in the art will be aware of suitable groups (e.g., halo,especially chloro and fluoro, amino, alkoxyl, mercapto, alkylmercapto,nitro, nitroso, sulfoxy, etc.).

3. Hetero substituents, that is, substituents which, while predominantlyhydrocarbon in character within the context of this invention, containatoms other than carbon present in a chain or ring otherwise composed ofcarbon atoms.

Importantly, the organo groups of the ligands have a sufficient numberof carbon atoms to render the compound soluble or dispersible in theoil. For example, the number of carbon atoms in each group willgenerally range between about 1 to about 100, preferably from about 1 toabout 30, and more preferably between about 4 to about 20. Preferredligands include dialkyldithiophosphate, alkylxanthate, anddialkyldithiocarbamate, and of these dialkyldithiocarbamate is morepreferred. Organic ligands containing two or more of the abovefunctionalities are also capable of serving as ligands and binding toone or more of the cores. Those skilled in the art will realize thatformation of the compounds of the present invention requires selectionof ligands having the appropriate charge to balance the core's charge.

Compounds having the formula MO₃S_(k)L_(n)Q_(z) have cationic coressurrounded by anionic ligands and are represented by structures such as

and have net charges of +4. Consequently, in order to solubilize thesecores the total charge among all the ligands must be −4. Fourmonoanionic ligands are preferred. Without wishing to be bound by anytheory, it is believed that two or more trinuclear cores may be bound orinterconnected by means of one or more ligands and the ligands may bemultidentate. Such structures fall within the scope of this invention.This includes the case of a multidentate ligand having multipleconnections to a single core. It is believed that oxygen and/or seleniummay be substituted for sulfur in the core(s).

Oil-soluble or dispersible trinuclear molybdenum compounds can beprepared by reacting in the appropriate liquid(s)/solvent(s) amolybdenum source such as (NH₄)₂Mo₃S₁₃.n(H₂O), where n varies between 0and 2 and includes non-stoichiometric values, with a suitable ligandsource such as a tetralkylthiuram disulfide. Other oil-soluble ordispersible trinuclear molybdenum compounds can be formed during areaction in the appropriate solvent(s) of a molybdenum source such as of(NH₄)₂Mo₃S₁₃.n(H₂O), a ligand source such as tetralkylthiuram disulfide,dialkyldithiocarbamate, or dialkyldithiophosphate, and a sulfurabstracting agent such cyanide ions, sulfite ions, or substitutedphosphines. Alternatively, a trinuclear molybdenum-sulfur halide saltsuch as [M′]₂[Mo₃S₇A₆], where M′ is a counter ion, and A is a halogensuch as Cl, Br, or I, may be reacted with a ligand source such as adialkyldithiocarbamate or dialkyldithiophosphate in the appropriateliquid(s)/solvent(s) to form an oil-soluble or dispersible trinuclearmolybdenum compound. The appropriate liquid/solvent may be, for example,aqueous or organic.

A compound's oil solubility or dispersibility may be influenced by thenumber of carbon atoms in the ligand's organo groups. In the compoundsof the present invention, at least 21 total carbon atoms should bepresent among all the ligand's organo groups. Preferably, the ligandsource chosen has a sufficient number of carbon atoms in its organogroups to render the compound soluble or dispersible in the lubricatingcomposition.

The terms “oil-soluble” or “dispersible” used herein do not necessarilyindicate that the compounds or additives are soluble, dissolvable,miscible, or capable of being suspended in the oil in all proportions.These do mean, however, that they are, for instance, soluble or stablydispersible in oil to an extent sufficient to exert their intendedeffect in the environment in which the oil is employed. Moreover, theadditional incorporation of other additives may also permitincorporation of higher levels of a particular additive, if desired.

The molybdenum compound is preferably an organo-molybdenum compound.Moreover, the molybdenum compound is preferably selected from the groupconsisting of a molybdenum dithiocarbamate (MoDTC), molybdenumdithiophosphate, molybdenum dithiophosphinate, molybdenum xanthate,molybdenum thioxanthate, molybdenum sulfide and mixtures thereof. Mostpreferably, the molybdenum compound is present as molybdenumdithiocarbamate. The molybdenum compound may also be a trinuclearmolybdenum compound.

Representative examples of suitable viscosity modifiers other thanpolymers (i), (ii) and (iii) are polyisobutylene, copolymers of ethyleneand propylene, polymethacrylates, methacrylate copolymers, copolymers ofan unsaturated dicarboxylic acid and a vinyl compound, interpolymers ofstyrene and acrylic esters, and partially hydrogenated copolymers ofstyrene/isoprene, styrene/butadiene, and isoprene/butadiene, as well asthe partially hydrogenated homopolymers of butadiene and isoprene.

A viscosity index improver dispersant functions both as a viscosityindex improver and as a dispersant. Examples of viscosity index improverdispersants include reaction products of amines, for example polyamines,with a hydrocarbyl-substituted mono- or dicarboxylic acid in which thehydrocarbyl substituent comprises a chain of sufficient length to impartviscosity index improving properties to the compounds. In general, theviscosity index improver dispersant may be, for example, a polymer of aC₄ to C₂₄ unsaturated ester of vinyl alcohol or a C₃ to C₁₀ unsaturatedmono-carboxylic acid or a C₄ to C₁₀ di-carboxylic acid with anunsaturated nitrogen-containing monomer having 4 to 20 carbon atoms; apolymer of a C₂ to C₂₀ olefin with an unsaturated C₃ to C₁₀ mono- ordi-carboxylic acid neutralised with an amine, hydroxyamine or analcohol; or a polymer of ethylene with a C₃ to C₂₀ olefin furtherreacted either by grafting a C₄ to C₂₀ unsaturated nitrogen-containingmonomer thereon or by grafting an unsaturated acid onto the polymerbackbone and then reacting carboxylic acid groups of the grafted acidwith an amine, hydroxy amine or alcohol. A preferred lubricating oilcomposition contains a dispersant composition of the present invention,base oil, and a viscosity index improver dispersant.

Pour point depressants, otherwise known as lube oil flow improvers(LOFI), lower the minimum temperature at which the fluid will flow orcan be poured. Such additives are well known. Other than the compoundsdescribed above as Polymer (iii), typical additives that improve the lowtemperature fluidity of the fluid are C₈ to C₁₈ dialkyl fumarate/vinylacetate copolymers, and polymethacrylates. Foam control can be providedby an antifoamant of the polysiloxane type, for example, silicone oil orpolydimethyl siloxane.

Some of the above-mentioned additives can provide a multiplicity ofeffects; thus for example, a single additive may act as adispersant-oxidation inhibitor. This approach is well known and need notbe further elaborated herein.

In the present invention it may be necessary to include an additivewhich maintains the stability of the viscosity of the blend. Thus,although polar group-containing additives achieve a suitably lowviscosity in the pre-blending stage it has been observed that somecompositions increase in viscosity when stored for prolonged periods.Additives which are effective in controlling this viscosity increaseinclude the long chain hydrocarbons functionalized by reaction withmono- or dicarboxylic acids or anhydrides which are used in thepreparation of the ashless dispersants as hereinbefore disclosed.

When lubricating compositions contain one or more of the above-mentionedadditives, each additive is typically blended into the base oil in anamount that enables the additive to provide its desired function.Representative effective amounts of such additives, when used. incrankcase lubricants, are listed below. All the values listed are statedas mass percent active ingredient. MASS % MASS % ADDITIVE (Broad)(Preferred) Metal Detergents  0.1-15  0.2-9 Corrosion Inhibitor   0-5   0-1.5 Metal Dihydrocarbyl Dithiophosphate  0.1-6  0.1-4 Antioxidant  0-5  0.01-2 Pour Point Depressant 0.01-5  0.01-1.5 Antifoaming Agent  0-5 0.001-0.15 Supplemental Antiwear Agents   0-1.0    0-0.5 FrictionModifier   0-5    0-1.5 Viscosity Modifier 0.01-10  0.25-3 BasestockBalance Balance

Fully formulated lubricating oil compositions of the present inventionhave a sulfur content of less than about 0.3 wt. %, preferably less thanabout 0.25 wt. % (e.g., less than 0.24 wt. %), more preferably less thanabout 0.20 wt. %, most preferably less than about 0.15 wt. % of sulfur.Preferably, the Noack volatility of the fully formulated lubricating oilcomposition (oil of lubricating viscosity plus all additives) will be nogreater than 12 mass %, such as no greater than 10 mass %, preferably nogreater than 8 mass %.

It may be desirable, although not essential, to prepare one or moreadditive concentrates comprising additives (concentrates sometimes beingreferred to as additive packages) whereby several additives can be addedsimultaneously to the oil to form the lubricating oil composition.

The final composition may employ from 5 to 25 mass %, preferably 5 to 18mass %, typically 10 to 15 mass % of the concentrate, the remainderbeing oil of lubricating viscosity.

This invention will be further understood by reference to the followingexamples, wherein all parts are parts by weight, unless otherwise notedand which include preferred embodiments of the invention.

EXAMPLES

The ability of a composition to control soot-induced viscosity increase,and thus, the ability of a composition to maintain soot in suspension,can be measured using bench tests, such as the test method describedherein. Base oil and additive components are blended to provideformulated oil. Carbon black powder is then added to the formulated oil.The kinematic viscosity at 100° C. of the carbon black dispersion ismeasured using the test method described in ASTM D445.

To demonstrate the response of detergents in the heavy duty dieselengines of the present invention, a comparison was made betweenkinematic viscosity increase of lubricating oil compositions in thepresence and absence of 1 wt. % pure sulfuric acid, using the carbonblack test procedure (3 wt. % carbon black), as described supra.Detergents were blended with base oil containing dispersant, antioxidantand antiwear agent (ZDDP). The results of the comparison are set forthin Table 1. TABLE 1 Example No. 1 2 3 Detergent Type Ca Phenate CaSulfonate Mg Sulfonate TBN 250 295 400 Detergent Amount (wt. %) 3.0 2.02.0 CB Kv @ 100° C. (cSt) 44.4 18.1 20.3 CB/Acid Kv @ 100° C. 166.4315.7 297.4 (cSt) CB Kv -CB/Acid Kv @ 122.0 297.6 277.1 100° C. (cst)

As shown in Table 1, the response of the detergents to the presence ofthe acid were dramatically different. Although the use of the sulfonatedetergents provided superior soot-induced kinematic viscosity propertiesin the absence of the acid, the presence of acid resulted in an increasein kinematic viscosity of from 1365% to 1644%. In contrast, thekinematic viscosity of the lubricant containing the phenate detergentincreased only 275% to a still acceptable 166.4 cSt.

The response of a lubricating oil compositions formulated withcommercial detergent inhibitor (DI) package containing dispersant,detergent (calcium phenate and calcium sulfonate), anti-oxidant,antiwear agent (ZDDP) and antifoamant to the presence of 1 wt. %sulfuric acid in a carbon black test (3 wt. % carbon black), asdescribed above, was compared to that of an identical lubricating oilcomposition, in which greater than 50% of the dispersant nitrogen wasrendered non-basic by reaction (capping) with EAA (ethyl acetoacetate).The results are set forth below, in Table 2. TABLE 2 Example No. 4 5Dispersant Amount (wt. %) 9.0 9.0 Dispersant Capping Agent None EAADispersant Nitrogen (wt. %) 0.108 0.73 finished oil Basic Nitrogen 3.851.5 (mmoles/100 g finished oil) % Non-Basic N 50 70 Dispersant HydroxylGroups 0 2-3* (mmoles/100 g finished oil) CB Kv @ 100° C. (cSt) 23.518.4 CB/Acid Kv @ 100° C. (cSt) 158.8 63.4 CB Kv -CB/Acid Kv @ 135.3 45100° C. (cSt)*tautomeric hydroxyl groups in equilibrium with keto-groups

As shown by the data of Table 2, the presence of the acid caused akinematic viscosity increase 576% in the lubricating oil compositioncontaining the uncapped dispersant. In contrast, the presence of theacid caused far less of an increase in the kinematic viscosity of thelubricating oil composition containing the capped dispersant.

To demonstrate the advantages of the present invention, a comparison wasmade between the kinematic viscosity increase of carbon back treatedlubricating oil in the presence, and in the absence, of 96% sulfuricacid. The addition of the acid (1 wt. % of 96% sulfuric acid) simulatesconditions in a heavy duty diesel engine provided with an EGR systemoperated in a condensing mode. In the testing described below, 3 wt. %of carbon black was added to lubricating oil compositions formulatedwith commercial detergent inhibitor (DI) package containing dispersant,detergent (calcium phenate and calcium sulfonate), anti-oxidant,anti-wear agent (ZDDP) and antifoamant and a commercial polymericviscosity modifier, as shown below.

SV151 is a styrene/diene copolymer available from Infineum USA L.P.ACRYLOID 954 is a multifunctional polymethacrylate viscosity modifieravailable from Rohmax USA Inc. HITEC 5777 and PA 1160 aremultifunctional OCP viscosity modifiers available commercially fromEthyl Corporation and Dutch Staaten Minen, respectively. The performanceof formulated oils containing these viscosity modifiers, which are eachwithin the scope of the present invention, was compared to that of aformulation containing a conventional, non-functionalized OCP copolymer(PTN 8011, available from ORONITE, a division of ChevronTexaco). In eachof the formulations, the amount of viscosity modifier was adjusted suchthat the lubricating oil compositions all qualified as a 15W40 grade oil(initial kv of 12.5 to 16.5 cSt), as specified in ASTM D445 test method.The results of the comparison are shown below, in Table 3. TABLE 3Example No. 6 7 8 9 10 11 12 13 14 15 16 DI Package 19.6 19.6 16.2516.25 16.25 16.25 16.25 16.25 16.25 16.25 16.25 (mass %) SV151 14.0 14.0(mass %) PTN8011 5.6 5.6 5.6 (mass %) ACRYLOID 954 6.0 6.0 (mass %)HITEC5777 6.0 6.0 (mass %) PA1160 6.0 6.0 (mass %) Base Oil 1* 74.678.15 77.75 77.75 77.75 (mass %) Base Oil 2** 66.4 69.75 78.15 77.7577.75 77.75 (mass %) CB Kv @ 100° C. (cSt) 25.79 37.00 24.46 19.20 19.8234.67 37.96 17.91 20.59 18.55 21.28 CB/Acid Kv @ 100° C. 28.14 324.0046.12 293.3 211.1 42.25 43.92 61.84 23.92 71.89 46.29 (cSt) CB Kv-CB/Acid Kv @ 2.35 287.00 21.66 274.10 191.28 7.58 5.96 43.93 3.33 53.3425.01 100° C. (cSt)*blend of Group I and Group II Base Oil(s) 84-85% saturates**Group II Base Oil(s) 92% saturates

As shown by the data of Table 3, the presence of acids increases thesoot-induced kinematic viscosity of the lubricating oil compositionscontaining the conventional OCP viscosity modifier by 875% (Example 7),to 1528% (Example 9), and resulted in extremely high absolute kinematicviscosities (211.1 cSt to 324.0 cSt). In contrast, lubricating oilcompositions containing Polymers (i), (ii) and (iii) showed an increasein kinematic viscosity of only 9% (Example 6) to 288% (Example 16), andacceptable absolute kinematic viscosity values of from 28.14 cSt to71.89 cSt.

The disclosures of all patents, articles and other materials describedherein are hereby incorporated, in their entirety, into thisspecification by reference. Compositions described as “comprising” aplurality of defined components are to be construed as includingcompositions formed by admixing the defined plurality of definedcomponents. The principles, preferred embodiments and modes of operationof the present invention have been described in the foregoingspecification. What applicants submit is their invention, however, isnot to be construed as limited to the particular embodiments disclosed,since the disclosed embodiments are regarded as illustrative rather thanlimiting. Changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

1. A lubricating oil composition having a sulfur content of less than0.3 wt. %, said lubricating oil composition comprising a major amount ofoil of lubricating viscosity, a minor amount of one or more highmolecular weight polymers comprising (i) olefin copolymers containingalkyl or aryl amine, or amide groups, nitrogen-containing heterocyclicgroups or ester linkages and/or (ii) acrylate or alkylacrylate copolymerderivatives having dispersing groups; and a minor amount of one or moreneutral and/overbased metal-containing detergents, wherein from about60% to 100% of the total amount of detergent surfactant is phenateand/or salicylate.
 2. The lubricating oil composition of claim 1,wherein said high molecular weight polymer comprises an olefin copolymercontaining aryl amine groups.
 3. The lubricating oil composition ofclaim 1, wherein said one or more neutral and/overbased metal-containingdetergents provide said lubricating oil composition with from about 6 toabout 50 mmoles of phenate surfactant per kilogram of finished oil. 4.The lubricating oil composition of claim 1, further comprising an amountof nitrogen-containing dispersant contributing no more than about 3.5mmoles of basic nitrogen per 100 grams of said lubricating oilcomposition, wherein greater than 50 wt. % of the total amount ofdispersant nitrogen is non-basic
 5. The lubricating oil composition ofclaim 4, wherein dispersant nitrogen is provided to said composition bydispersant, or a mixture of dispersants derived from hydrocarbonpolymers having an average Mn of from about 1500 to about 3000, and saiddispersant, or mixture of dispersants contributes to said lubricatingoil composition from about 0.10 to about 0.18 wt. % of nitrogen, basedon the total weight of the lubricating oil composition.
 6. Thelubricating oil composition of claim 4, wherein at least one of saidnitrogen-containing dispersant is derived from highly reactivepolyisobutylene, having a terminal vinylidene content of at least 65%.7. The lubricating oil composition of claim 6, wherein said highlyreactive polyisobutylene has an average M_(n) of from about 1500 toabout
 3000. 8. The lubricating oil composition of claim 7, wherein saiddispersant, or mixture of dispersants contributes to said lubricatingoil composition from about 0.10 to about 0.18 wt. % of nitrogen, basedon the total weight of the lubricating oil composition.
 9. Thelubricating oil composition of claim 4, wherein at least a portion ofthe basic nitrogen of said nitrogen-containing dispersant is renderednon-basic by reacting said nitrogen-containing dispersant with acompound selected from alkyl acetoacetates; formic acid; glycolic acid;alkyl and alkylene carbonates; maleic anhydride and succinic anhydride.10. The lubricating oil composition of claim 9, wherein dispersantprovides the lubricating oil composition with from about 1 to about 7mmols of hydroxyl per 100 grams of finished oil.
 11. The lubricating oilcomposition of claim 1, wherein said detergent is selected from mixedsurfactant phenate/salicylate detergents, sulfur-free phenatedetergents, and mixtures thereof
 12. The lubricating oil composition ofclaim 1, wherein said oil of lubricating viscosity has a VI of at least120.
 13. The lubricating oil composition of claim 1, wherein said oil oflubricating viscosity has a saturates content of at least
 90. 14. Alubricating oil composition of claim 1, having a 0 W or 5 W viscositygrade.
 15. A lubricating oil composition of claim 1, substantially freeof sulfur-containing phenate detergent.
 16. A lubricating oilcomposition of claim 1, having a Noack volatility of less than 12 mass%.
 17. A lubricating oil composition of claim 15, having a Noackvolatility of less than 10 mass %.
 18. A lubricating oil composition ofclaim 1, having a phosphorus content of less than 800 ppm.
 19. Alubricating oil composition of claim 18, having a phosphorus content offrom about 300 ppm to about 800 ppm.
 20. The lubricating oil compositionof claim 1, further comprising at least one an aminic antioxidant,phenolic antioxidant, or a combination thereof.
 21. A method ofoperating a compression ignited engine provided with an exhaust gasrecirculation system which method comprises lubricating said engine witha lubricating oil composition of claim
 1. 22. The method of claim 21,wherein said compression ignited engine is fuelled by a diesel fuelcontaining less than 50 ppm of sulfur.
 23. The method of claim 21,wherein said engine is a heavy duty diesel engine and said exhaust gasrecirculation system cools intake air and/or exhaust gas recirculationstreams to below the dew point for at least 10% of the time said engineis in operation.
 24. A lubricating oil composition having a sulfurcontent of less than 0.3 wt. %, said lubricating oil compositioncomprising a major amount of oil of lubricating viscosity selected fromGroup I, Group II and Group III mineral oil, and mixtures thereof, aminor amount of one or more high molecular weight polymers comprising(i) copolymers of hydrogenated poly(monovinyl aromatic hydrocarbon) andpoly (conjugated diene), wherein the hydrogenated poly(monovinylaromatic hydrocarbon) segment comprises at least about 20 wt. % of thecopolymer; (ii) olefin copolymers containing alkyl or aryl amine, oramide groups, nitrogen-containing heterocyclic groups or ester linkagesand/or (iii) acrylate or alkylacrylate copolymer derivatives havingdispersing groups; a minor amount of a nitrogen-containing dispersantderived from highly reactive polyisobutylene, having a terminalvinylidene content of at least 65%.
 25. The lubricating oil compositionof claim 24, wherein said high molecular weight polymer is an olefincopolymer containing aryl amine groups.
 26. The lubricating oilcomposition of claim 24, further comprising and a minor amount of one ormore neutral and/overbased metal-containing detergents selected frommixed surfactant phenate/salicylate detergents, phenate detergents,salicylate detergents and mixtures thereof.
 27. The lubricating oilcomposition of claim 26, wherein from about 60% to 100% of the totalamount of detergent surfactant is phenate and/or salicylate.
 28. Thelubricating oil composition of claim 26, wherein said detergents areselected from the group consisting of mixed surfactantphenate/salicylate detergents, sulfur-phenate detergents, and mixturesthereof.
 29. The lubricating oil composition of claim 24, wherein saidhighly reactive polyisobutylene has an average M_(n) of from about 1500to about
 3000. 30. The lubricating oil composition of claim 29, whereinsaid nitrogen-containing dispersant contribute from about 0.10 to about0.18 wt. % of nitrogen, based on the total weight of the lubricating oilcomposition, and no more than about 3.5 mmoles of basic nitrogen per 100grams of said lubricating oil composition, wherein greater than 50 wt. %of the total amount of dispersant nitrogen is non-basic.
 31. Thelubricating oil composition of claim 30, wherein at least a portion ofthe basic nitrogen of said nitrogen-containing dispersant is renderednon-basic by reacting said nitrogen-containing dispersant with acompound selected from alkyl acetoacetates; formic acid; glycolic acid;alkyl and alkylene carbonates; maleic anhydride and succinic anhydride.32. The lubricating oil composition of claim 24, wherein said oil oflubricating viscosity has a VI of at least
 120. 33. The lubricating oilcomposition of claim 24, wherein said oil of lubricating viscosity has asaturates content of at least
 90. 34. A lubricating oil composition ofclaim 24, having a 0 W or 5 W viscosity grade.
 35. A lubricating oilcomposition of claim 24, having a Noack volatility of less than 12 mass%.
 36. A lubricating oil composition of claim 24, having a phosphoruscontent of less than 800 ppm.
 37. The lubricating oil composition ofclaim 24, further comprising at least one an aminic antioxidant,phenolic antioxidant, or a combination thereof.
 38. A method ofoperating a compression ignited engine provided with an exhaust gasrecirculation system which method comprises lubricating said engine witha lubricating oil composition of claim
 24. 39. The method of claim 25,wherein said compression ignited engine is fuelled by a diesel fuelcontaining less than 50 ppm of sulfur.
 40. The method of claim 38,wherein said engine is a heavy duty diesel engine and said exhaust gasrecirculation system cools intake air and/or exhaust gas recirculationstreams to below the dew point for at least 10% of the time said engineis in operation.
 41. A lubricating oil composition comprising a majoramount of oil of lubricating viscosity, a minor amount of one or morehigh molecular weight polymers comprising (i) copolymers of hydrogenatedpoly(monovinyl aromatic hydrocarbon) and poly (conjugated diene),wherein the hydrogenated poly(monovinyl aromatic hydrocarbon) segmentcomprises at least about 20 wt. % of the copolymer; (ii) olefincopolymers containing alkyl or aryl amine, or amide groups,nitrogen-containing heterocyclic groups or ester linkages and/or (iii)acrylate or alkylacrylate copolymer derivatives having dispersinggroups; and a minor amount of one or more neutral and/overbasedmetal-containing detergents selected from the group consisting of mixedsurfactant phenate/salicylate detergents, sulfur-free phenatedetergents, and mixtures thereof.
 42. The lubricating oil composition ofclaim 41, wherein said high molecular weight polymer is an olefincopolymer containing aryl amine groups.
 43. The lubricating oilcomposition of claim 41, wherein from about 60% to 100% of the totalamount of detergent surfactant is phenate and/or salicylate.
 44. Alubricating oil composition of claim 41, substantially free ofsulfur-containing phenate detergent.
 45. The lubricating oil compositionof claim 41, wherein said one or more neutral and/overbasedmetal-containing detergents provide said lubricating oil compositionwith from about 6 to about 50 mmoles of phenate surfactant per kilogramof finished oil.
 46. The lubricating oil composition of claim 41,further comprising an amount of nitrogen-containing dispersantcontributing no more than about 3.5 mmoles of basic nitrogen per 100grams of said lubricating oil composition, wherein greater than 50 wt. %of the total amount of dispersant nitrogen is non-basic
 47. Thelubricating oil composition of claim 46, wherein dispersant nitrogen isprovided to said composition by dispersant, or a mixture of dispersantsderived from hydrocarbon polymers having an average M_(n) of from about1500 to about 3000, and said dispersant, or mixture of dispersantscontributes to said lubricating oil composition from about 0.10 to about0.18 wt. % of nitrogen, based on the total weight of the lubricating oilcomposition.
 48. The lubricating oil composition of claim 41, furthercomprising at least one of said nitrogen-containing dispersant isderived from highly reactive polyisobutylene, having a terminalvinylidene content of at least 65%.
 49. The lubricating oil compositionof claim 48, wherein said highly reactive polyisobutylene has an averageMn of from about 1500 to about
 3000. 50. The lubricating oil compositionof claim 49, wherein said dispersant, or mixture of dispersantscontributes to said lubricating oil composition from about 0.10 to about0.18 wt. % of nitrogen, based on the total weight of the lubricating oilcomposition.
 51. The lubricating oil composition of claim 49, wherein atleast a portion of the basic nitrogen of said nitrogen-containingdispersant is rendered non-basic by reacting said nitrogen-containingdispersant with a compound selected from alkyl acetoacetates; formicacid; glycolic acid; alkyl and alkylene carbonates; maleic anhydride andsuccinic anhydride.
 52. The lubricating oil composition of claim 51,wherein dispersant provides the lubricating oil composition with fromabout 1 to about 7 mmols of hydroxyl per 100 grams of finished oil. 53.The lubricating oil composition of claim 41, wherein said lubricatingoil composition has a sulfur content of less than 0.3 wt. %.
 54. Thelubricating oil composition of claim 41, wherein said oil of lubricatingviscosity has a VI of at least
 120. 55. The lubricating oil compositionof claim 41, wherein said oil of lubricating viscosity has a saturatescontent of at least
 90. 56. A lubricating oil composition of claim 41,having a 0 W or 5 W viscosity grade.
 57. A lubricating oil compositionof claim 41, substantially free of sulfur-containing phenate detergent.58. A lubricating oil composition of claim 41, having a Noack volatilityof less than 12 mass %.
 59. A lubricating oil composition of claim 58,having a Noack volatility of less than 10 mass %.
 60. A lubricating oilcomposition of claim 41, having a phosphorus content of less than 800ppm.
 61. A lubricating oil composition of claim 60, having a phosphoruscontent of from about 300 ppm to about 800 ppm.
 62. The lubricating oilcomposition of claim 41, further comprising at least one an aminicantioxidant, phenolic antioxidant, or a combination thereof.
 63. Amethod of operating a compression ignited engine provided with anexhaust gas recirculation system which method comprises lubricating saidengine with a lubricating oil composition of claim
 41. 64. The method ofclaim 63, wherein said compression ignited engine is fuelled by a dieselfuel containing less than 50 ppm of sulfur.
 65. The method of claim 63,wherein said engine is a heavy duty diesel engine and said exhaust gasrecirculation system cools intake air and/or exhaust gas recirculationstreams to below the dew point for at least 10% of the time said engineis in operation.